Wafer probe station having environment control enclosure

ABSTRACT

A wafer probe station is equipped with an integrated environment control enclosure substantially surrounding a supporting surface for holding a test device, such enclosure limiting fluid communication between the interior and exterior of the enclosure and preferably also providing EMI shielding and a dark environment. The limited communication between the interior and exterior of the enclosure is kept substantially constant despite positioning movement of either the supporting surface or probes. The positioning mechanisms for the supporting surface and probes each are located at least partially outside of the enclosure.

[0001] This application is a continuation of U.S. patent applicationSer. No. 10/268,244, filed Oct. 9, 2002, which is a continuation of Ser.No. 10/068,728, filed Feb. 6, 2002, which is a continuation of U.S.patent application Ser. No. 09/886,353, filed Jun. 20, 2001, which is acontinuation of U.S. patent application Ser. No. 08/790,969, filed Jan.29, 1997, now U.S. Pat. No. 6,313,649, which is a continuation of U.S.patent application Ser. No. 08/641,029, filed Apr. 29, 1996, now U.S.Pat. No. 5,604,444, which is a continuation of U.S. patent applicationSer. No. 08/417,982, filed Apr. 6, 1995, now U.S. Pat. No. 5,532,609,which is a division of U.S. patent application Ser. No. 08/245,581,filed May 18, 1994, now U.S. Pat. No. 5,434,512, which is a division ofU.S. patent application Ser. No. 07/896,853 filed Jun. 11, 1992, nowU.S. Pat. No. 5,345,170.

BACKGROUND OF THE INVENTION

[0002] The present invention is directed to probe stations for makinghighly accurate measurements of high-speed, large scale integratedcircuits at the wafer level, and of other electronic devices. Moreparticularly, the invention relates to such a probe station having anenvironment control enclosure for limiting the communication of thewafer-supporting chuck and probes with outside influences such aselectromagnetic interference (EMI), air, and/or light.

SUMMARY OF THE INVENTION

[0003] The probe station is equipped with an integrated environmentcontrol enclosure substantially surrounding a supporting surface forholding a test device, such enclosure limiting fluid communicationbetween the interior and exterior of the enclosure and preferably alsoproviding EMI shielding and a dark environment. The limitedcommunication between the interior and exterior of the enclosure is keptsubstantially constant despite positioning movement of either thesupporting surface or probes. The positioning mechanisms for thesupporting surface and probes are each located at least partiallyoutside of the enclosure so that mechanical movement of each of thepositioning mechanisms outside of the enclosure causes proportionalmechanical movement of the surface or probe.

[0004] According to another aspect of the invention, the environmentcontrol enclosure has an upper portion extending above the supportingsurface and a side portion substantially surrounding the supportingsurface, the supporting surface being movable laterally with respect tothe top of the side portion.

[0005] According to another aspect of the invention, the environmentcontrol enclosure has an opening with a closable door for substitutingdifferent test devices on the supporting surface in a manner compatiblewith the positioning and environment control functions.

[0006] The foregoing and other objectives, features, and advantages ofthe invention will be more readily understood upon consideration of thefollowing detailed description of the invention, taken in conjunctionwith the accompanying drawings.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

[0007]FIG. 1 is a partial front view of an exemplary embodiment of awafer probe station constructed in accordance with the presentinvention.

[0008]FIG. 2 is a top view of the wafer probe station of FIG. 1.

[0009]FIG. 2A is a partial top view of the wafer probe station of FIG. 1with the enclosure door shown partially open.

[0010]FIG. 3 is a partially sectional and partially schematic front viewof the probe station of FIG. 1.

[0011]FIG. 3A is an enlarged sectional view taken along line 3A-3A ofFIG. 3.

[0012]FIG. 4 is a top view of the sealing assembly where the motorizedpositioning mechanism extends through the bottom of the enclosure.

[0013]FIG. 5A is an enlarged top detail view taken along line 5A-5A ofFIG. 1.

[0014]FIG. 5B is an enlarged top sectional view taken along line 5B-5Bof FIG. 1.

[0015]FIG. 6 is a partially schematic top detail view of the chuckassembly, taken along line 6-6 of FIG. 3.

[0016]FIG. 7 is a partially sectional front view of the chuck assemblyof FIG. 6.

[0017]FIG. 8 is a partially sectional side view of a probe holder andprobe.

[0018]FIG. 9 is a partially sectional bottom view taken along line 9-9of FIG. 8.

DESCRIPTION OF THE INVENTION General Arrangement of Probe Station

[0019] With reference to FIGS. 1, 2 and 3, an exemplary embodiment ofthe probe station of the present invention comprises a base 10 (shownpartially) which supports a platen 12 through a number of jacks 14 a, 14b, 14 c, 14 d which selectively raise and lower the platen verticallyrelative to the base by a small increment (approximately one-tenth of aninch) for purposes to be described hereafter. Also supported by the base10 of the probe station is a motorized positioner 16 having arectangular plunger 18 which supports a movable chuck assembly 20 forsupporting a wafer or other test device. The chuck assembly 20 passesfreely through a large aperture 22 in the platen 12 which permits thechuck assembly to be moved independently of the platen by the positioner16 along X, Y and Z axes, i.e. horizontally along twomutually-perpendicular axes X and Y, and vertically along the Z axis.Likewise, the platen 12, when moved vertically by the jacks 14, movesindependently of the chuck assembly 20 and the positioner 16.

[0020] Mounted atop the platen 12 are multiple individual probepositioners such as 24 (only one of which is shown), each having anextending member 26 to which is mounted a probe holder 28 which in turnsupports a respective probe 30 for contacting wafers and other testdevices mounted atop the chuck assembly 20. The probe positioner 24 hasmicrometer adjustments 34, 36 and 38 for adjusting the position of theprobe holder 28, and thus the probe 30, along the X, Y and Z axesrespectively, relative to the chuck assembly 20. The Z axis is exemplaryof what is referred to herein loosely as the “axis of approach” betweenthe probe holder 28 and the chuck assembly 20, although directions ofapproach which are neither vertical nor linear, along which the probetip and wafer or other test device are brought into contact with eachother, are also intended to be included within the meaning of the term“axis of approach.” A further micrometer adjustment 40 adjustably tiltsthe probe holder 28 to adjust planarity of the probe with respect to thewafer or other test device supported by the chuck assembly 20. As manyas twelve individual probe positioners 24, each supporting a respectiveprobe, may be arranged on the platen 12 around the chuck assembly 20 soas to converge radially toward the chuck assembly similarly to thespokes of a wheel. With such an arrangement, each individual positioner24 can independently adjust its respective probe in the X, Y and Zdirections, while the jacks 14 can be actuated to raise or lower theplaten 12 and thus all of the positioners 24 and their respective probesin unison.

[0021] An environment control enclosure is composed of an upper boxportion 42 rigidly attached to the platen 12, and a lower box portion 44rigidly attached to the base 10. Both portions are made of steel orother suitable electrically conductive material to provide EMIshielding. To accommodate the small vertical movement between the twobox portions 42 and 44 when the jacks 14 are actuated to raise or lowerthe platen 12, an electrically conductive resilient foam gasket 46,preferably composed of silver or carbon-impregnated silicone, isinterposed peripherally at their mating juncture at the front of theenclosure and between the lower portion 44 and the platen 12 so that anEMI, substantially hermetic, and light seal are all maintained despiterelative vertical movement between the two box portions 42 and 44. Eventhough the upper box portion 42 is rigidly attached to the platen 12, asimilar gasket 47 is preferably interposed between the portion 42 andthe top of the platen to maximize sealing.

[0022] With reference to FIGS. 5A and 5B, the top of the upper boxportion 42 comprises an octagonal steel box 48 having eight side panelssuch as 49 a and 49 b through which the extending members 26 of therespective probe positioners 24 can penetrate movably. Each panelcomprises a hollow housing in which a respective sheet 50 of resilientfoam, which may be similar to the above-identified gasket material, isplaced. Slits such as 52 are partially cut vertically in the foam inalignment with slots 54 formed in the inner and outer surfaces of eachpanel housing, through which a respective extending member 26 of arespective probe positioner 24 can pass movably. The slitted foampermits X, Y and Z movement of the extending members 26 of each probepositioner, while maintaining the EMI, substantially hermetic, and lightseal provided by the enclosure. In four of the panels, to enable agreater range of X and Y movement, the foam sheet 50 is sandwichedbetween a pair of steel plates 55 having slots 54 therein, such platesbeing slidable transversely within the panel housing through a range ofmovement encompassed by larger slots 56 in the inner and outer surfacesof the panel housing.

[0023] Atop the octagonal box 48, a circular viewing aperture 58 isprovided, having a recessed circular transparent sealing window 60therein. A bracket 62 holds an apertured sliding shutter 64 toselectively permit or prevent the passage of light through the window. Astereoscope (not shown) connected to a CRT monitor can be placed abovethe window to provide a magnified display of the wafer or other testdevice and the probe tip for proper probe placement during set-up oroperation. Alternatively, the window 60 can be removed and a microscopelens (not shown) surrounded by a foam gasket can be inserted through theviewing aperture 58 with the foam providing EMI, hermetic and lightsealing.

[0024] The upper box portion 42 of the environment control enclosurealso includes a hinged steel door 68 which pivots outwardly about thepivot axis of a hinge 70 as shown in FIG. 2A. The hinge biases the doordownwardly toward the top of the upper box portion 42 so that it forms atight, overlapping, sliding peripheral seal 68 a with the top of theupper box portion. When the door is open, and the chuck assembly 20 ismoved by the positioner 16 beneath the door opening as shown in FIG. 2A,the chuck assembly is accessible for loading and unloading.

[0025] With reference to FIGS. 3 and 4, the sealing integrity of theenclosure is likewise maintained throughout positioning movements by themotorized positioner 16 due to the provision of a series of four sealingplates 72, 74, 76 and 78 stacked slidably atop one another. The sizes ofthe plates progress increasingly from the top to the bottom one, as dothe respective sizes of the central apertures 72 a, 74 a, 76 a and 78 aformed in the respective plates 72, 74, 76 and 78, and the aperture 79 aformed in the bottom 44 a of the lower box portion 44. The centralaperture 72 a in the top plate 72 mates closely around the bearinghousing 18 a of the vertically-movable plunger 18. The next plate in thedownward progression, plate 74, has an upwardly-projecting peripheralmargin 74 b which limits the extent to which the plate 72 can slideacross the top of the plate 74. The central aperture 74 a in the plate74 is of a size to permit the positioner 16 to move the plunger 18 andits bearing housing 18 a transversely along the X and Y axes until theedge of the top plate 72 abuts against the margin 74 b of the plate 74.The size of the aperture 74 a is, however, too small to be uncovered bythe top plate 72 when such abutment occurs, and therefore a seal ismaintained between the plates 72 and 74 regardless of the movement ofthe plunger 18 and its bearing housing along the X and Y axes. Furthermovement of the plunger 18 and bearing housing in the direction ofabutment of the plate 72 with the margin 74 b results in the sliding ofthe plate 74 toward the peripheral margin 76 b of the next underlyingplate 76. Again, the central aperture 76 a in the plate 76 is largeenough to permit abutment of the plate 74 with the margin 76 b, butsmall enough to prevent the plate 74 from uncovering the aperture 76 a,thereby likewise maintaining the seal between the plates 74 and 76.Still further movement of the plunger 18 and bearing housing in the samedirection causes similar sliding of the plates 76 and 78 relative totheir underlying plates into abutment with the margin 78 b and the sideof the box portion 44, respectively, without the apertures 78 a and 79 abecoming uncovered. This combination of sliding plates and centralapertures of progressively increasing size permits a full range ofmovement of the plunger 18 along the X and Y axes by the positioner 16,while maintaining the enclosure in a sealed condition despite suchpositioning movement. The EMI sealing provided by this structure iseffective even with respect to the electric motors of the positioner 16,since they are located below the sliding plates.

Chuck Assembly

[0026] With particular reference to FIGS. 3, 6 and 7, the chuck assembly20 is of a unique modular construction usable either with or without anenvironment control enclosure. The plunger 18 supports an adjustmentplate 79 which in turn supports first, second and third chuck assemblyelements 80, 81 and 83, respectively, positioned at progressivelygreater distances from the probe(s) along the axis of approach. Element83 is a conductive rectangular stage or shield 83 which detachablymounts conductive elements 80 and 81 of circular shape. The element 80has a planar upwardly-facing wafer-supporting surface 82 having an arrayof vertical apertures 84 therein. These apertures communicate withrespective chambers separated by 0-rings 88, the chambers in turn beingconnected separately to different vacuum lines 90 a, 90 b, 90 c (FIG. 6)communicating through separately-controlled vacuum valves (not shown)with a source of vacuum. The respective vacuum lines selectively connectthe respective chambers and their apertures to the source of vacuum tohold the wafer, or alternatively isolate the apertures from the sourceof vacuum to release the wafer, in a conventional manner. The separateoperability of the respective chambers and their corresponding aperturesenables the chuck to hold wafers of different diameters.

[0027] In addition to the circular elements 80 and 81, auxiliary chuckssuch as 92 and 94 are detachably mounted on the corners of the element83 by screws (not shown) independently of the elements 80 and 81 for thepurpose of supporting contact substrates and calibration substrateswhile a wafer or other test device is simultaneously supported by theelement 80. Each auxiliary chuck 92, 94 has its own separateupwardly-facing planar surface 100, 102 respectively, in parallelrelationship to the surface 82 of the element 80. Vacuum apertures 104protrude through the surfaces 100 and 102 from communication withrespective chambers within the body of each auxiliary chuck. Each ofthese chambers in turn communicates through a separate vacuum line and aseparate independently-actuated vacuum valve (not shown) with a sourceof vacuum, each such valve selectively connecting or isolating therespective sets of apertures 104 with respect to the source of vacuumindependently of the operation of the apertures 84 of the element 80, soas to selectively hold or release a contact substrate or calibrationsubstrate located on the respective surfaces 100 and 102 independentlyof the wafer or other test device. An optional metal shield 106 mayprotrude upwardly from the edges of the element 83 to surround the otherelements 80, 81 and the auxiliary chucks 92, 94.

[0028] All of the chuck assembly elements 80, 81 and 83, as well as theadditional chuck assembly element 79, are electrically insulated fromone another even though they are constructed of electrically conductivemetal and interconnected detachably by metallic screws such as 96. Withreference to FIGS. 3 and 3A, the electrical insulation results from thefact that, in addition to the resilient dielectric O-rings 88,dielectric spacers 85 and dielectric washers 86 are provided. These,coupled with the fact that the screws 96 pass through oversizedapertures in the lower one of the two elements which each screw joinstogether thereby preventing electrical contact between the shank of thescrew and the lower element, provide the desired insulation. As isapparent in FIG. 3, the dielectric spacers 85 extend over only minorportions of the opposing surface areas of the interconnected chuckassembly elements, thereby leaving air gaps between the opposingsurfaces over major portions of their respective areas. Such air gapsminimize the dielectric constant in the spaces between the respectivechuck assembly elements, thereby correspondingly minimizing thecapacitance between them and the ability for electrical current to leakfrom one element to another. Preferably, the spacers and washers 85 and86, respectively, are constructed of a material having the lowestpossible dielectric constant consistent with high dimensional stabilityand high volume resistivity. A suitable material for the spacers andwashers is glass epoxy, or acetal homopolymer marketed under thetrademark Delrin by E.I. DuPont.

[0029] With reference to FIGS. 6 and 7, the chuck assembly 20 alsoincludes a pair of detachable electrical connector assemblies designatedgenerally as 108 and 110, each having at least two conductive connectorelements 108 a, 108 b and 110 a, 110 b, respectively, electricallyinsulated from each other, with the connector elements 108 b and 110 bpreferably coaxially surrounding the connector elements 108 a and 110 aas guards therefor. If desired, the connector assemblies 108 and 110 canbe triaxial in configuration so as to include respective outer shields108 c, 110 c surrounding the respective connector elements 108 b and 110b, as shown in FIG. 7. The outer shields 108 c and 110 c may, ifdesired, be connected electrically through a shielding box 112 and aconnector supporting bracket 113 to the chuck assembly element 83,although such electrical connection is optional particularly in view ofthe surrounding EMI shielding enclosure 42, 44. In any case, therespective connector elements 108 a and 110 a are electrically connectedin parallel to a connector plate 114 matingly and detachably connectedalong a curved contact surface 114 a by screws 114 b and 114 c to thecurved edge of the chuck assembly element 80. Conversely, the connectorelements 108 b and 110 b are connected in parallel to a connector plate116 similarly matingly connected detachably to element 81. The connectorelements pass freely through a rectangular opening 112 a in the box 112,being electrically insulated from the box 112 and therefore from theelement 83, as well as being electrically insulated from each other. Setscrews such as 118 detachably fasten the connector elements to therespective connector plates 114 and 116.

[0030] Either coaxial or, as shown, triaxial cables 118 and 120 formportions of the respective detachable electrical connector assemblies108 and 110, as do their respective triaxial detachable connectors 122and 124 which penetrate a wall of the lower portion 44 of theenvironment control enclosure so that the outer shields of the triaxialconnectors 122, 124 are electrically connected to the enclosure. Furthertriaxial cables 122 a, 124 a are detachably connectable to theconnectors 122 and 124 from suitable test equipment such as aHewlett-Packard 4142B modular DC source/monitor or a Hewlett-Packard4284A precision LCR meter, depending upon the test application. If thecables 118 and 120 are merely coaxial cables or other types of cableshaving only two conductors, one conductor interconnects the inner(signal) connector element of a respective connector 122 or 124 with arespective connector element 108 a or 110 a, while the other conductorconnects the intermediate (guard) connector element of a respectiveconnector 122 or 124 with a respective connector element 108 b, 110 b.

[0031] In any case, the detachable connector assemblies 108, 110, due totheir interconnections with the two connector plates 114, 116, provideimmediately ready-to-use signal and guard connections to the chuckassembly elements 80 and 81, respectively, as well as ready-to-useguarded Kelvin connections thereto. For applications requiring onlyguarding of the chuck assembly, as for example the measurement oflow-current leakage from a test device through the element 80, it isnecessary only that the operator connect a single guarded cable 122 afrom a test instrument such as a Hewlett-Packard 4142B modular DCsource/monitor to the detachable connector 122 so that a signal line isprovided to the chuck assembly element 80 through the connector element108 a and connector plate 114, and a guard line is provided to theelement 81 through the connector element 108 b and connector plate 116.Alternatively, if a Kelvin connection to the chuck assembly is desiredfor low-voltage measurements, such as those needed for measurements oflow capacitance, the operator need merely attach a pair of cables 122 aand 124 a to the respective connectors 122, 124 from a suitable testinstrument such as a Hewlett-Packard 4284A precision LCR meter, therebyproviding both source and measurement lines to the element 80 throughthe connector elements 108 a and 110 a and connector plate 114, andguarding lines to the element 81 through the connector elements 108 band 110 b and connector plate 116.

Probe Assembly

[0032] With reference to FIGS. 5B, 8 and 9, respective individuallymovable probes 30 comprising pairs of probe elements 30 a are supportedby respective probe holders 28 which in turn are supported by respectiveextending portions 26 of different probe positioners such as 24. Atopeach probe positioner 24 is a shield box 126 having a pair of triaxialconnectors 128, 130 mounted thereon with respective triaxial cables 132entering each triaxial connector from a suitable test instrument asmentioned previously. Each triaxial connector includes a respectiveinner connector element 128 a, 130 a, an intermediate connector element128 b, 130 b, and an outer connector element 128 c, 130 c in concentricarrangement. Each outer connector element 128 c, 130 c terminates byconnection with the shield box 126. Conversely, the inner connectorelements 128 a, 130 a, and the intermediate connector elements 128 b,130 b, are connected respectively to the inner and outer conductors of apair of coaxial cables 134, 136 which therefore are guarded cables. Eachcable 134, 136 terminates through a respective coaxial connector 138,140 with a respective probe element 30 a having a center conductor 142surrounded by a guard 144. In order to provide adequate shielding forthe coaxial cables 134, 136, especially in the region outside of theoctagonal box 48, an electrically-conductive shield tube 146 is providedaround the cables 134, 136 and electrically connected through the shieldbox 126 with the outer connector element 128 c, 130 c of the respectivetriaxial connectors 128, 130. The shield tube 146 passes through thesame slit in the foam 50 as does the underlying extending member 26 ofthe probe positioner 24. Thus, each individually movable probe 30 hasnot only its own separate individually movable probe holder 28 but alsoits own individually movable shield 146 for its guarded coaxial cables,which shield is movable in unison with the probe holder independently ofthe movement of any other probe holder by any other positioningmechanism 24. This feature is particularly advantageous because suchindividually movable probes are normally not equipped for both shieldedand guarded connections, which deficiency is solved by the describedstructure. Accordingly, the probes 30 are capable of being used with thesame guarding and Kelvin connection techniques in a ready-to-use manneras is the chuck assembly 20, consistently with full shielding despitethe individual positioning capability of each probe 30.

[0033] The terms and expressions which have been employed in theforegoing specification are used therein as terms of description and notof limitation, and there is no intention, in the use of such terms andexpressions, of excluding equivalents of the features shown anddescribed or portions thereof, it being recognized that the scope of theinvention is defined and limited only by the claims which follow.

1. A probe station comprising: (a) a chuck for supporting a test device;(b) at least one support for a probe to contact said test device; (c) anenclosure having a side member and an electrically conductive lowermember having a substantially horizontal surface spaced vertically belowsaid chuck; and (d) a member defining an aperture for receiving apositioner secured to said chuck, said aperture being capable ofrelative lateral movement with respect to said side member.
 2. The probestation of claim 1 where said lower member comprises said member.
 3. Theprobe station of claim 1 having a positioner extending through saidaperture and where said member comprises overlapping, relativelyslidable members extending laterally beneath said surface, said slidablemembers being of different sizes and defining openings of differentsizes, and wherein one of said openings is said aperture.
 4. The probestation of claim 3, wherein said enclosure has an upper member extendingsubstantially laterally over said chuck, and said side member has a topthat is substantially immovable laterally relative to said upper member.5. The probe station of claim 3 wherein said positioner includes a motorassembly beneath said slidable members for moving said positioner. 6.The probe station of claim 1 wherein said enclosure includes a door forselectively accessing said chuck.
 7. The probe station of claim 1, saidenclosure substantially shielding said chuck against electromagneticinterference.
 8. The probe station of claim 1, said enclosuresubstantially shielding said chuck against light.
 9. The probe stationof claim 1, said enclosure limiting fluid communication between theinterior and exterior of said enclosure.